1. Field of the Invention
This invention relates to a process for the production of water-free detergent mixtures, in which amines are alkylated in the presence of nonionic surfactants, to the products obtained by this process and to their use in surface-active compositions.
2. Statement of Related Art
Amphoteric or zwitterionic surfactants are highly compatible with the skin and show excellent cleaning properties. Accordingly, they are particularly suitable for use in the production of a number of surface-active products. In the most simple case, they are produced by reaction of secondary or tertiary amines with sodium chloroacetate to form alkyl betaines. The reaction of fatty acid amidoamines or imidazolines with sodium chloroacetate leads to the formation of amphoteric surfactants of the glycinate type. If an acrylate is used as the alkylating agent, aminopropionates are formed. Compounds of the type mentioned are described in a number of synoptic articles among which only Parf. Cosm. Atom. 70, 67 (1986), HAPPI, 70 (November 1986) and Soap Cosm. Chem. Spec. 46 (April 1990) are cited here.
A particular concern in the production of amphoteric or zwitterionic surfactants is to produce highly concentrated but free-flowing products in order thus to minimize transport and storage costs. In addition, the basically excellent compatibility of the products with the skin must not be impaired by traces of unreacted alkylating agent and phase separation through an excessive electrolyte content must be avoided.
There has been no shortage of attempts in the past to solve one or more of the problems mentioned. Thus, DE-A 29 26 479 (Goldschmidt) describes a process for the production of alkyl amidobetaines in which the residual content of alkylating agent is minimized by carrying out the reaction at a pH value of 7.5 to 10.5. The teaching of DE-A 20 63 424 (Rewo), which describes pH regulation for the alkylation of imidazolines, points in the same direction.
According to DE-A1 40 40 887 (Goldschmidt), the quaternization reaction involved in the production of free-flowing, aqueous betaine dispersions is carried out in aqueous or alcoholic solution with addition of anionic surfactants. In addition, it is known from GB-A 20 22 125 that C.sub. 12/14 cocoalkyl dimethylamine can be alkylated with sodium chloroacetate in the presence of an aqueous solution of sodium lauryl sulfate. However, it is expressly pointed out in both documents that the presence of water during the alkylation reaction is absolutely essential because otherwise non-flowable products with a lamellar liquid crystal structure would be formed. Accordingly, the processes mentioned give highly concentrated, but not water-free surfactant pastes.
Another process for the production of flowable and pumpable betaines with an active substance content of at least 70% by weight is known from EP-B10 243 619 (Goldschmidt). According to this document, amidoamines with a melting point of at most 30.degree. C. are used as the sole starting materials and the quaternization reaction is carried out with potassium or ammonium chloroacetate in an organic solvent which may contain at most 20% by weight of water. However, a process such as this is hardly suitable for operation on an industrial scale because the necessary separation of the solvent from the useful product on completion of the alkylation reaction would involve considerable outlay on equipment.
In addition, it is known from EP-B1 0 302 329 (Goldschmidt) that free-flowing betaine pastes with a content of around 40% by weight can be produced by concentrating the aqueous betaine solutions obtained by conventional quaternization processes to the desired water content by evaporation and subsequently adjusting the pH to a value of 1 to 4.5 by addition of mineral acid.
According to EP-A2 0 353 580 (Goldschmidt), concentrated, free-flowing, aqueous solutions of betaines optionally containing lower aliphatic alcohols are produced by carrying out the quaternization in aqueous or aqueous-alcoholic solution with addition of nonionic surfactants in such a quantity that the resulting solution has a nonionic surfactant content of, preferably, 3 to 20% by weight. Suitable nonionic surfactants are, above all, fatty acid polyethylene oxide esters. Fatty alcohol alkoxylates with an HLB value of 14 to 20 are mentioned as other suitable, but specifically not preferred surfactants. However, this document teaches carrying out the quaternization in the presence of water and/or alcohols, preferably ethanol, and adding extremely hydrophilic, nonionic surfactants, for example polysorbates containing 120 ethylene oxide units, to the betaines before, but preferably after, the quaternization to reduce their viscosity. Accordingly, water-free products cannot be produced by this process either. Another disadvantage is that compounds of betaines and extremely hydrophilic nonionic surfactants are unavoidably obtained, the nonionic surfactants in question being unsuitable for cosmetic products or dishwashing detergents on account of their inadequate foaming.
Accordingly, the problem addressed by the present invention was to provide amphoteric surfactants in water-free form and, at the same time, to avoid the disadvantages of the prior art.